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Sympathetic nervous system
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===Information transmission=== [[File:Sympathetic Nervous System.jpg|thumb|223x223px|Sympathetic nervous system β Information transmits through it affecting various organs.]] [[Messages]] travel through the sympathetic nervous system in a bi-directional flow. [[efferent nerve fiber|Efferent]] messages can simultaneously trigger changes in different body parts. For example, the sympathetic nervous system can accelerate [[heart rate]]; widen [[bronchial]] passages; decrease [[motility]] (movement) of the [[large intestine]]; constrict blood vessels; increase [[peristalsis]] in the [[oesophagus]]; cause [[pupillary dilation]], piloerection ([[goose bumps]]) and perspiration ([[sweating]]); and raise blood pressure. One exception is with certain blood vessels, such as those in the cerebral and coronary arteries, which dilate (rather than constrict) with increased sympathetic tone. This is because of a proportional increase in the presence of Ξ²<sub>2</sub> adrenergic receptors rather than Ξ±<sub>1</sub> receptors. Ξ²<sub>2</sub> receptors promote vessel dilation instead of constriction like Ξ±1 receptors. An alternative explanation is that the primary (and direct) effect of sympathetic stimulation on coronary arteries is vasoconstriction followed by a secondary vasodilation caused by the release of vasodilatory metabolites due to the sympathetically increased cardiac inotropy and heart rate. This secondary vasodilation caused by the primary vasoconstriction is termed functional sympatholysis, the overall effect of which on coronary arteries is dilation.<ref name="Klabunde">{{cite book | vauthors=Klabunde RE | title=Cardiovascular physiology concepts | publisher=Lippincott Williams & Wilkins/Wolters Kluwer | publication-place=Philadelphia, PA | date=2012 | isbn=978-1-4511-1384-6 | oclc=712765593 | language=hu | page=160}}</ref> The target synapse of the postganglionic neuron is mediated by [[adrenergic receptors]] and is activated by either [[norepinephrine]] (noradrenaline) or [[epinephrine]] (adrenaline).
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